PEP is a 3C compound which serves as primary CO2 acceptor in the mesophyll cell cytoplasm of C4 plants like Maize, Sugarcane, Sorghum etc.
PEP is able to rapidly fix carbon at very low concentrations of hydrogen carbonate in presence of Phosphoenolpyruvate carboxylase enzyme the addition of bicarbonate(HCO3−) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate
PEP+HCO3−→oxaloacetate+Pi